Component 1: The group nature of college student drinking has been both widely recognized and largely ignored within the research community. Concepts such as peer pressure have been discussed with barely any acknowledgement of the potentially complex group dynamics that may play vital roles on alcohol consumption and its consequences. To date, observable group characteristics such as size or gender composition have been the main focus of group drinking research. While the study of these variables represents an essential first step in tackling the comple phenomenon of group drinking, a comprehensive conceptualization of natural drinking groups (NDGs) has not been proposed yet. The most difficult barrier to studying social groups is that they form, exist, and disperse at times when researchers are unlikely to have contact with them. We propose a research program that will develop and test a paradigm for measuring processes of naturally occurring collegiate drinking groups. The series of proposed measurements will incorporate qualitative analyses of interviews and diaries from samples of Southern California college students with recent NDG experience. This formative research will guide the development of the third proposed study, in which a total of 100 NDGs will be surveyed three times. This survey will combine self-reports of concurrent, retrospective, prospective NDG experiences, and direct observational measures of drinking behaviors (breath alcohol concentration tests). Of particular interest will be variables that pertain to group construction, intra-group social roles, group cohesion and conflict, interpersonal relationships, and drinking behaviors. The data will be examined with sophisticated data analysis techniques (multilevel modeling and social network analysis). Component 2: Put together, these three studies will contribute to develop an innovative conceptualization of collegiate natural drinking groups. Through this research, a line of investigation will begin to identify important variables that may serve as powerful loci for public health interventions designed to reduce the risky behaviors of young drinkers.